Prior art may be exemplified by products of the companies em-tec GmbH, D-86923 Finning or Transonic Systems Inc., New York 14850, USA.
Thus, the company em-tec GmbH offers a clamp-on transducer for measuring a flow in extracorporeal tubing systems, as available for checking on the website http://www.em-tec.de of said company. The sensor placed in a housing is clamped on a tube by a click closure, and the measurement is thus taken non-invasively. Applications can be found in medicine, e. g. in measurements which have to be taken at a heart-lung machine in intensive care medicine.
A similar transducer is mentioned as a bypass flowmeter and tubing sensor by the company Transonic Systems Inc., as described in HT100 Bypass Flowmeter & Tubing Sensor, “Surgery/ICU Products” on the website http://www.transonic.com.
This solution also uses a clamp-on tubing sensor, which may be sterilized and attached to flexible tubes in operating theatres. Here, a section of a flexible tube is located in a measuring channel, without applying external mechanical pressure, wherein the ultrasonic signals are coupled in the direction of the liquid flow or against it.
The previously known solutions of the prior art, as exemplified above, make use of an arrangement of clamp-on sensors in which transmitter/receiver transducer and the electronic evaluation system are physically separated, which may cause crosstalk of the signals on the connection line between them. A measurement on smaller tube sizes has not been offered so far.
The disadvantages of the examples of the prior art, as mentioned above, must therefore be overcome.
Therefore, the object of the invention is to propose a device for the contactless flow measurement of fluids for applications in medicine, industry and others, in which the sound emitting and receiving ceramics (piezoelectric elements) are integrated in such way that they are decoupled from the other components, to the end that the signals of the ceramics do not interfere with each other, fewer transverse vibrations or directional effects are caused by using composite ceramics with an optimized width/thickness ratio, and a comparatively simple electronic evaluation system—without using an A/D transducer—is provided for the device as well as the measuring space in the housing of the device should embodied as a measuring channel in such way that, by exchanging few components in the sense of a modular concept, the insertion of a flexible tube within a defined range of usable diameters into the preferably rectangular measuring channel is made in such way that the surface for coupling sound signals into the fluid flowing in a flexible tube is as large as possible, wherein the assessment of received measurement signals should bring a high level of significance—even in consideration of a varying temperature and therefore a different viscosity of the fluid flowing through the flexible tube.
The object of the invention is achieved as follows, referring to patent claim 1 with regard to the basic inventive concept. Further embodiments of the invention are shown in claims 2 through 8.
The device is basically designed as a sensor for measuring the flow rate of a sound-transparent medium in a flexible tube of a low diameter, preferably within an outside diameter range of at least 3.5 mm, in a so-called clamp-on design.
It consists of a compact, in particular plastic housing with a hinged cover made of the same material, attached to its top side, which is fixed by means of a spring-loaded rest hook in the closed state of the housing. On the outside of the housing, opposite the closure of the hinged cover, there is a service interface for the connection to peripheral imaging systems or for voltage supply, as the case may be.
When the hinged cover is opened, a rectangular measuring channel, open to the outside, which extends over the entire width of this surface, becomes visible in the upper area of the housing. Its dimensioning is made in such way that a flexible tube of a defined diameter may be inserted by slight mechanical pressure, through which the wall of the flexible tube fits to the walls of the measuring channel and the underside of the hinged cover covering the measuring channel from above in a rectangular shape when the hinged cover is closed. In the centre of the measuring channel, in the upper housing area limiting the compact housing to the top, there is a measuring cell with ceramics (piezoelectric elements) facing each other diagonally in pairs, which are held in lateral parts, which measuring cell is limited from below by a base plate in the installation space of the compact housing. The base plate in its consistency also forms a bottom limiting the measuring channel overall.
Furthermore, a feature of the invention can bee seen in that the housing of the device has distances at least twice as long in relation the width of the measuring channel for a tube inlet and for a tube outlet for inserting the flexible tube. In this way, a tube inlet or outlet of a defined length, as a section of the measuring channel, contributes to calming the fluid flowing through the flexible tube, which improves measuring stability.
In order that a measuring result of received signals always gives a real picture of the flow volume of a sound-transparent fluid, also the temperature of the latter must be considered because temperature-related changes in viscosity can accelerate or slow down the flow. Therefore, a temperature sensor, the measuring values of which are used as a coefficient for determining the flow volume by way of calculation, is attached to one side of the measuring cell.
An outstanding feature of the invention is that the measuring channel may be enlarged in its cross-section—without changing its width—, starting from a square up to a standing rectangle, by the modular exchange of the base plate, which limits the measuring channel and the measuring cell on the bottom side, which allows to detect flexible tubes with a low outside diameter, from at least 3.5 mm and beyond, within defined limits.
Therein, the dimensions of the measuring cell, consisting in particular of the ceramics integrated into the lateral parts at a defined distance, remain unchanged to the extent technically reasonable. The ceramics are in particular designed as composite ceramics, and the individual elements of the measuring cell are not connected to each other in a compact casting. A joint casting with the electronic evaluation system, which is located below the measuring cell in the installation space for electronic modules, is not present either. Such decoupled design of the device, which may also be regarded as a miniaturisation in this order, avoids negative influences on the sending and receiving of measuring signals by crosstalk of the ceramics.
In addition, for improving the measuring quality, it is provided that the compact housing of the device together with the hinged cover is made of a material which provides shielding against electromagnetic waves from the environment. An appropriate plastic material is suitable for this.
Below the measuring cell there is an installation space for electronic components in the housing of the device.
It comprises:                a) a multiplexer for a transmitted signal,        b) a multiplexer for a received signal,        c) an adjustable amplifier for received signals in connection with a zero-crossing comparator,        d) a time to digital converter (TDC), which is configured and controlled by a microcontroller (MC),        e) a transmitter,        f) a microcontroller (MC) as central control unit,        g) an output circuit,        h) a service interface, and        i) an operating voltage supply.        